Sedative/hypnotic abuse among the elderly is a growing concern. Chronic insomnia occurs in 25-30% of 65-79 year olds and survey reports of sleep disturbances in the elderly correspond to a disproportionate use of sleep medication. Sleep medications can lose their efficacy after long-term use and can result in rebound insomnia upon withdrawal, sleepiness during the day, and complications when combined with other medications. Polysomnographic (PSG) changes in the elderly corresponding to subjective sleep complaints include: increases in nocturnal wake-time and substantial decreases in the amount and amplitude of slow-wave sleep (SWS). Slow-wave sleep, which has been considered to have physiological restorative properties, also is significantly suppressed by benzodiazepine hypnotic medications. There is a need for alternative methods for improving sleep overall and increasing slow-wave sleep in particular, in the elderly. Fourteen elderly female volunteers who complain of difficulty initiating and/or maintaining sleep will participate in a 9-nigh sleep study. Baseline actigraphic and sleep diary data will be collected for two weeks prior to the studies to evaluate objective and subjective sleep parameters and to confirm insomnia. Passive Body Heating (PBH) will be compared to a no-heat bath to study its effects on sleep parameters. The PBH intervention will involve having the subjects sit in a tub filled with 40 degrees C water for 20-30 minutes until their body temperature rises 1.0 degree C. Water temperature will be luke warm (37.5 degrees C) in the control, no-heat condition. PSG monitoring will be done on two separate series. the first lasting five consecutive days and the second lasting four consecutive days. A three-day rest period will be allowed between the two series. The first series will consist of a screening night, two baseline and two treatment nights of one of the two conditions (heat or no-heat). The second series will consist of two baseline and two treatment nights of the other condition. The order of treatment will be counterbalanced. Objective measures of sleep will be quantified using standard sleep scoring criteria. Changes in sleep continuity and slow-wave sleep will be inferred from changes in sleep efficiency while amplitude and density of slow wave sleep will be quantified using power spectral analysis. Subjective measures of sleep will be taken using a post-sleep questionnaire and a visual analog scale. Core body temperature and motor activity will be recorded continuously using ambulatory monitoring systems. The present study is designed to determine if PBH increases SWS and improves the continuity and quality of sleep in elderly insomniacs. Results may generalize to a geriatric population previous findings in young adults of elevations in core body temperature leading to altered objective and subjective sleep parameters. The proposed PBH technique should achieve the same effect without the added risks associated with having elderly individuals participate in strenuous exercise in order to elevate core body temperature. If the PBH procedure improves sleep measures, then it may be a useful non-pharmacologic adjunct method for treating insomnia in the elderly.